Salonen had addressed a padded envelope containing the device to two Cryptopay employees.

It was delivered at some point in November 2017 to an office in Hackney, which had housed an accountancy firm previously used by Cryptopay.

Several months later, on 8 March 2018, a worker at the office began opening the package but did not continue when they became suspicious of what was inside.

‘Sheer luck’

The Met Police Counter Terrorism Command then began its investigation.

“It was due to sheer luck that the recipient ripped opened the package in the middle rather than using the envelope flap which would have activated the device,” said its head, Commander Clarke Jarrett.

DNA found in the package did not match information on UK databases, so it was analysed by Interpol.

“Through these inquiries, it was identified that the DNA matched those of Salonen, who was known to Swedish authorities,” the Met says.